Advances in industrial Ethernet have made it
possible to get just about any device to communicate over a
network. A USB-to-serial server, for example, will network-enable
legacy serial devices that were built before the USB specification
came into existence. Engineers have worked out the ways to smoothly
transfer data between whatever protocols are appropriate for the
task at hand, be it TCP/IP to Modbus or Profibus to USB. At the
physical layer, a network may be a mix of copper cable and fiber
optics, and it may sprawl across numerous buildings or an entire
campus.

Steady improvements in wireless technology are
now allowing a greater number of devices to establish wireless
connectivity with the same reliability already achieved by cable
communications. Better still, it is becoming possible to make these
kinds of connections in increasingly difficult environments. That
doesn’t mean, however, that you can’t step on
your own toes and prevent it from happening. This article will
describe some of the things that you can do to frustrate your own
plans.

1. Forget about signal echo

The typical open radio frequencies (900 MHz and
2.4 GHz) used for wireless data connectivity applications have a
reasonable penetration range in buildings built with wood frame and
drywall. But watch what happens when you try to set up a wireless
network in an older building where the walls are made of plaster on
a galvanized wire mesh. The CIA offices in Moscow can be assumed to
have more advanced methods for interfering with radio signals. But
for any ordinary purposes, plaster on wire mesh isn’t
half bad.

Dense building materials like concrete will also
interfere with radio signals, especially if the concrete is
reinforced with metal rebar. Large metal objects like industrial
machinery will do the same. This bounce can redirect the data
signal and return it to the original transmitter, causing an "echo"
or "multi-path". First-generation wireless systems were easily
confused by this type of interference and would cancel transmission
all together. The result was a state referred to as "radio null"
and it prevented data communication.

Several transmission and modulation schemes have
been developed to counter the effects of echo. One of the best is
FHSS (Frequency Hopping Spread Spectrum), in which data is
transmitted on a single channel, but the channel is constantly
changing or "hopping". This scheme requires low bandwidth. Another
excellent choice is DSSS (Direct Sequence Spread Spectrum), in
which data is transmitted simultaneously over every available
channel, making it a bit more reliable in "noisy" environments.
DSSS has the disadvantage of being more bandwidth intensive.

Note that all of the wireless transmitters,
nodes and equipment on your network must support the same
transmission scheme to connect properly.

2. Ignore electromagnetic interference
(EMI)

The electromagnetic emissions created by large
motors, heavy equipment, high power generation and usage, and other
typical industrial machinery can create extremely high levels of
"noise", which interferes with wireless connectivity. In these
"noisy" environments, transmitters and remote nodes are unable to
"hear" each other, resulting in frequent data loss. Frequency
Hopping Spread Spectrum (FHSS) and Direct Sequence Spread Spectrum
(DSS) will help with this problem as well.

3. Just park your antenna anywhere and walk
away

Antennas increase their effective power by
focusing the radiated energy in the desired direction. Using the
correct antenna not only focuses power, it reduces the amount of
power broadcast into areas where it is not needed. But one symptom
of the increasing popularity of wireless is the fact that everyone
seeks out the highest convenient places to mount their antennas.
It’s not uncommon to arrive at a job site to find that
other antennas are already sprouting all over your installation
point. Even if you suspect that these systems are spread spectrum
and likely to be using other ISM or licensed frequency bands,
you’ll still want to maximize the distance between their
antennas and your own. Most antennas broadcast in a horizontal
pattern, so vertical separation is more meaningful than horizontal
separation. Try to separate antennas with like-polarization by a
minimum of two wavelengths, which is about 26 in. (0.66 m) at 900
MHz, or 10 inches (0.25 m) at 2.4 GHz.

Antennas can be directional, sending and
receiving signals in a single direction. Examples would include
dish, Yagi, and panel antennas. The advantage of a directional
antenna is its greater range and its ability to focus coverage
where it is needed. Antennas can also be omnidirectional, sending
and receiving the signal in a linear radius. The advantage here is
the antenna’s ability to communicate with a large number
of nodes.

Proper antenna choice and location will have a
big impact on your wireless connectivity.

4. Ignore range considerations

Wireless connectivity range is determined by
four elements:

• Transmit
power: Transmit power is the amount of power that is emitted
from the antenna port of the wireless device. Proprietary RF is
regulated in the US for up to 1 W. This provides substantial
benefits when long ranges are needed, because the higher the
transmit power, the "louder" the signal, and the farther it can
travel.

• Receiver
sensitivity: Sensitivity defines how well remote receivers
can "hear" the signal. Sensitivity is significantly impacted by
antenna type and hardware configurations.

• Line of
sight (LOS): As radio waves are elliptical, the fewer
barriers along the LOS between receiver and transmitter, the
better. Frequency and transmit power levels have the most impact on
how well the signal can negotiate physical and EMI line of sight
barriers.

• Data
volume: Data rate and volume will impact your range. Large
data packets are more difficult to transmit than smaller packets
and will typically reduce range.

Choose equipment that will address these issues
in a manner appropriate for the task at hand (see Fig. 1).

Fig. 1: Range considerations must be
addressed by equipment in ways appropriate for the task.

5. Don’t worry about security

Chances are that your industrial network will be
at least tangentially connected to an office LAN. Bear in mind that
any Wi-Fi-enabled computer can connect to multiple networks at the
same time. A hacker could use one of your employees’
laptops to access your network. An employee could bring your
network down simply by wandering onto the wrong screen and hitting
the wrong commands.

Don’t assume that your network is safe
just because your premises are off the beaten path. Separate the
office and industrial LANs with firewalls and employ robust
security standards. Early wireless security standards like WEP
(Wired Equivalent Privacy) turned out to be too weak —
hackers didn’t have much trouble getting around them. You
should consider more powerful standards like Extensible
Authentication Protocol and Tunneled Extensible Authentication
Protocol.

Also don’t assume that your wireless
equipment has built-in security features. Be certain, one way or
the other. Deploy inspection-type firewalls (such as packet
filters) to control any access that is based on IP source address,
destination address, and port number.

Change your passwords on a regular basis, and
don’t make them easy to guess. A recent study has shown
that some very popular passwords include
“password,” “querty,”
“abc123,” and “123456.” You
can do better than that.

6. Install office-grade equipment

Industrial environments are harder on wireless
equipment than any office would ever be. In a steel mill, for
example, excessive heat, heavy vibration, and high levels of EMI
will dramatically shorten the useful lifespan of your wireless
equipment. You get what you pay for in this world, and using
office-grade networking equipment to save small amounts of money up
front will turn out to be a huge mistake when you have to pay for
it later with downtime and repairs. ■

About the author

Andy Ross is currently the director of wireless
applications for B&B Electronics and is an expert in M2M device
networking. After serving as general manager of Mosaic
Semiconductor, Ross moved to DPAC Technologies as director of
technology, where he was responsible for the definition and
development of advanced 3D packaging. Ross has served on the board
of the JEDEC Solid State Technology Association, which sets the
standards for the packaging and interfaces of semiconductors. He
currently holds five US patents in advanced packaging technologies.
Ross graduated from Sheffield Hallam University in the United
Kingdom.